The present invention relates to fraction collectors, such as fraction collectors used in the field of liquid chromatography.
Numerous fraction collectors including a rotatably mounted turntable for supporting a plurality of collection tubes are known, for example through U.S. Pat. No. 4,862,932. In fraction collectors of the turntable type, a liquid is sequentially discharged into the collection tubes through an outlet conduit, such as a hollow needle. The outlet conduit is mounted on an arm reaching over the turntable. Typically, the arm can swing around a vertical post to be positioned over different radial rows of collecting tubes.
Similarly, fraction collectors wherein collecting tubes are arranged in a rectangular grid pattern and an outlet conduit is positioned over each collecting tube by a rectilinear positioning movement are known. In such fraction collectors, herein referred to as xe2x80x9cX-Y-collectorsxe2x80x9d, it is usually the outlet conduit that is moved with respect to the collecting tubes. An example of such a fraction collector is shown in U.S. Pat. No. 4,422,151.
An example of an X-Y-collector wherein both a receptacle supporting table and a delivery head are moved linearly, in transverse directions with respect to each other, is described in U.S. Pat. No. 4,077,444.
In a conventional turntable fraction collector it is possible to dispense liquid volumes into a selected number of receptacles, for example test tubes. The dispensing means, typically a metal or plastic tube extending from an arm reaching over the receptacles, essentially is held at rest with respect to the turntable, while the receptacles change place by rotating the turntable when switching from one receiving receptacle to the next.
The turntable fraction collector is useful in many applications. However, in certain cases X-Y-collectors are more suitable. For example, when handling a large number of receptacles, bench space is more effectively used when arranging the receptacles in a X-Y-pattern. There are also popular standardized receptacle plates, so called microtiter plates, that have small recesses arranged in a X-Y-pattern. Conventional turntable fraction collectors cannot handle such plates.
A conventional X-Y-collector has a table for holding the receptacles (or microtiter plates or similar), and is further equipped with means for moving a dispensing tube over and between the receptacles. Typically, the moving of the dispensing tube is achieved by the use of a set of stepping motors. Furthermore, it is known to control the stepping motors to position the dispensing tube over any receptacle in any desired order.
However, compared to the turntable collector, a X-Y-collector requires a longer attachment tubing, since the equipment providing the liquid is stationary with respect to the receptacles, and the tubing therefore has to follow the dispensing tube to any receptacle. Especially in high-resolution liquid chromatography this is a disadvantage since a long tubing give separated components in the liquid longer time to diffuse within the liquid flow, and consequently the precision of the separation is negatively affected.
When switching from one receptacle to the next spillage could occur due to an outflow through the dispensing tube between the receptacles. Under certain conditions such spillage should be avoided, for example when collecting fractions of a liquid holding very valuable substances wherein it is important to collect each individual drop. In such cases, a conventional X-Y-collector is disadvantageous since the movement of the dispensing tube is apt to shake off any drop developed at the end of the dispensing tube during the switching movement.
The disadvantages of the conventional X-Y-collector, as described above, could be overcome with a X-Y-collector wherein the receptacle table is moved in the X and Y directions, instead of the dispensing tube. However, with such a construction valuable bench-space is lost.
It is the object of the present invention to provide a bench space saving fraction collector with the ability to position a selected receptacle among a plurality of receptacles, regardless of the pattern in which the receptacles are arranged, under a dispensing tube connected to a liquid feeding system
This object is achieved with a device of the type described herein.
The fraction collector according to the invention combines the features of the substantially resting outlet tube, short attachment tubing length and small bench space requirement connected with a turntable collector, with the features of X-Y-arrangement ability and dispensing of liquid in a selectable sequence of receptacles connected with a X-Y-collector.
Thus, the fraction collector of the invention is useful for receptacles of any size (including of mutually different sizes) arranged in any two-dimensional pattern, eg. in circular rows of test tubes as well as microtiter plates.
Since the receptacles are moving during a receptacle change, rather than the dispensing tube, the risk of losing drops is reduced as compared to the conventional X-Y-collector.
As the dispensing tube is at rest with respect to the receptacles it can be positioned very near the outlet of any liquid feeding device, such as the outlet of a liquid chromatography column, thereby providing for the shortest possible attachment tubing.
All these advantageous features as well as others that are obvious from the following detailed description of preferred embodiments of the invention are obtained with a fraction collector requiring a limited amount of bench-space.